Lampadas was the site of a Bene Gesserit? Keep. It was one of the many planets the Honored Matres? attacked on their return from the Scattering to the Old Empire. 7,622,014 Reverend Mothers were posted at Lampadas at the time of the Honored Matre attack and despite the efforts of the Bashar Burzmali only one Reverend Mother - Lucilla - managed to escape the planet alive, though she did carry the shared memories of all her deceased Sisterhood on Lampadas.
Sources: Chapterhouse: Dune?
More: Dune wikia,